All UWP packages are broken on .NET 9 because of Uno references

[Sergio0694]

Describe the bug

I was testing the new builds from main and noticed all UWP packages are broken on .NET 9:

The core of the issue is that we have a net9.0 TFM pulling in Uno dependencies. We should not do this. The official guidance for packages that have UI framework dependencies is to have different packages for different UI frameworks. Uno should have their own packages as well. We need 4:

• *.Uwp: UWP .NET Native and .NET 9
• *.Uwp.Uno: UWP XAML Uno flavor
• *.WinUI: WinUI 3
• *.WinUI.Uno: WinUI 3 Uno flavor

As a short term solution, we can add a net9.0-windows10.0.26100.0 TFM to work around the issue for UWP .NET 9 consumers.

Code Platform

• UWP
• WinAppSDK / WinUI 3
• Web Assembly (WASM)
• Android
• iOS
• MacOS
• Linux / GTK